This application is based on applications Nos. 2001-020624, 2000-362020, and 2001-005428 filed in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a photoelectric conversion device. In particular, this invention relates to a photoelectric conversion device using numerous crystalline semiconductor particles.
2. Description of the Related Art
FIGS. 12-14 show photoelectric conversion devices using crystalline semiconductor particles that have been proposed so far.
FIG. 12 illustrates a solar cell in which a first conductive layer 33 is disposed over the surface of a substrate 32 which has been formed in a configuration with a periodically (regularly) indented pattern, and parts 31a of spherical or long cylindrical semiconductor crystals 31 are brought into electrical contact with the first conductive layer 33, while the other parts 31b of the spherical or long cylindrical semiconductor crystals 31 are brought into electrical contact with a second conductive layer 34. (Refer to Japanese Unexamined Patent Publication (Kokai) No. 2000-22184.) In FIG. 12, the numerals 35, 36, and 37 denote a high-reflection film, a spin-on-glass SOG1, and a spin-on-glass SOG2, respectively.
In the device shown in FIG. 12, since the spherical semiconductor crystals 31 are arranged according to the indented surface configuration of the substrate 32, it is necessary to form an insulator 37 (for example, spin-on-glass SOG2) along the indented contours of the substrate 32. Since such insulator formation cannot be performed by general printing methods, it has a problem of lowered productivity. In addition, since the device is arranged such that each of the recesses on the substrate 32 has one spherical semiconductor crystal 31 mounted thereon, mounting of the spherical semiconductor crystals 31 becomes difficult when they are reduced in size. It is therefore impossible in the above case to reduce the size of the spherical semiconductor crystals 31. Accordingly, reduction in quantity of the semiconductor used as the raw material cannot be accomplished, which causes the problem of low productivity and high cost.
FIG. 13 illustrates another known photoelectric conversion device (U.S. Pat. No. 5,419,782). In this photoelectric conversion device, apertures are formed in a first aluminum foil 44, and p-type silicon spheres 45 with n-type outer portions 46 are connected to the apertures. Then, the n-type outer portions 46 in the lower portions of the spheres are removed. An oxide coating 47 is applied to the surface of aluminum 48 and the oxide coating 47 in the lower portions of the spheres are removed so that the p-type silicon spheres 45 are joined to a second aluminum foil 48. A transparent coating 49 is provided at the top surface. In this device, due to the coating 49 having a configuration which abruptly changes at the lowest point, light incident on locations where the p-type silicon spheres 45 are absent is directed to the p-type silicon spheres 45, thereby improving the photoelectric conversion efficiency.
The photoelectric conversion device shown in FIG. 13 intends to improve the photoelectric conversion efficiency by the arrangement being such that the coating 49 has a configuration which abruptly changes at the lowest point so as to form a V-shape. However, since forming such a coating having a configuration that changes abruptly at the lowest point is technically difficult, it would cause poor productivity. In addition, the material of the coating 49 deteriorates when exposed to sunlight for long duration of time, gradually lowering the photoelectric conversion efficiency.
FIG. 14 illustrates a photoelectric conversion device in which an aluminum film 52 is formed around a steel substrate 51, and crushed silicon particles 54 are joined to the aluminum film 52, over which an insulator layer 53, n-type silicon portions 55 and a transparent conductive layer 56 are formed in succession (U.S. Pat. No. 4,514,580).
The disclosure of the photoelectric conversion device shown in FIG. 14 lacks detailed descriptions regarding preferred arrangements of the crystalline semiconductor particles 54 and preferred shapes of peripheral regions around the crystalline semiconductor particles 54. Accordingly, this device fails to efficiently utilize light incident on the peripheral regions around the crystalline semiconductor particles 54, causing the problem of low photoelectric conversion efficiency.
It is an object of the present invention to provide a photoelectric conversion device with high efficiency and high productivity.
(1) A photoelectric conversion device according to the present invention comprises: a lower electrode; numerous crystalline semiconductor particles of one conductivity type deposited on the lower electrode; an insulator formed among the crystalline semiconductor particles; and a semiconductor layer of the opposite conductivity type formed on the side of the upper portions of the crystalline semiconductor particles, wherein the insulator is formed of a translucent material, and the surface of the lower electrode comprises a roughened surface.
The above arrangement allows light that has been incident on the surface of the lower electrode to be scattered and directed to the crystalline semiconductor particles, thereby improving the photoelectric conversion efficiency, as well as it can enhance the adhesiveness between the lower electrode and the insulator formed thereon.
(2) Another photoelectric conversion device according to the present invention comprises: a lower electrode; numerous crystalline semiconductor particles of one conductivity type deposited on the lower electrode; an insulator formed among the crystalline semiconductor particles; and a semiconductor layer of the opposite conductivity type formed on the side of the upper portions of the crystalline semiconductor particles, wherein the insulator is formed of a translucent material, and a protruding portion comprising a reflective material is formed between the crystalline semiconductor particles.
The photoelectric conversion device according to the above arrangement allows incident light to be scattered by the protruding portion and directed to the crystalline semiconductor particles so that the photoelectric conversion efficiency is improved. Accordingly, a photoelectric conversion device with high efficiency and high productivity can be realized.
(3) Another photoelectric conversion device according to this invention comprises: a lower electrode; numerous crystalline semiconductor particles of one conductivity type deposited on the lower electrode; an insulator formed among the crystalline semiconductor particles; and a semiconductor layer of the opposite conductivity type formed on the side of the upper portions of the crystalline semiconductor particles, wherein the crystalline semiconductor particles are arranged such that a crystalline semiconductor particle is located on a straight line that perpendicularly crosses a line segment connecting central parts of other crystalline semiconductor particles that are adjacent to each other approximately at the midpoint of the line segment.
The photoelectric conversion device arranged as above enables light incident on peripheral regions around the crystalline semiconductor particles to contribute to the generation of electricity so that high photoelectric conversion efficiency can be achieved.
Structural details of these inventions are hereinafter described referring to the appended drawings.